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| United States Patent |
5,741,521
|
|
Knight
, et al.
|
April 21, 1998
|
Biodegradable controlled release amylaceous material matrix
Abstract
A biodegradable or digestible matrix is provided suitable for use as a
controlled release of an agriculturally active agent such as insecticides,
fungicides, fertilizers, plant growth regulants, etc. The matrix comprises
an amylaceous material optionally in association with a synthetic polymer
and is formed under elevated temperature and pressure.
| Inventors:
|
Knight; Adrian Timothy (Lane Cove, AU);
Anderson; Thomas Peter (Manly West, AU);
Ahmetagic; Mirsad Ahmet (Albany Creek, AU)
|
| Assignee:
|
Goodman Fielder Limited (AU);
Incitec Limited (AU)
|
| Appl. No.:
|
454093 |
| Filed:
|
May 30, 1995 |
Foreign Application Priority Data
| Current U.S. Class: |
424/488; 71/64.01; 71/64.03; 71/64.07; 264/176.1; 264/184; 264/186; 264/211; 424/409; 424/486; 424/487; 424/499; 424/501; 424/757; 504/358 |
| Intern'l Class: |
A01N 025/10; A01N 025/14; A01N 025/34; B29C 047/00 |
| Field of Search: |
424/486,488,487,499,501,409
71/64.01,64.03,64.07,DIG. 1
|
References Cited
| Foreign Patent Documents |
| 2887689 | Aug., 1989 | AU.
| |
| 2227245 | Jul., 1990 | GB.
| |
Primary Examiner: Webman; Edward J.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part application of Ser. No.
07/838,802, filed May 11, 1992, now abandoned.
Claims
We claim:
1. A method for manufacture of a biodegradable matrix shape for use in
connection with the controlled release delivery of an agriculturally
active agent, said method comprising the steps of:
(a) providing a composition comprising an amylaceous material having an
amylose content of at least 50% w/w and water, said water being present in
an amount of from about 2 to about 30% w/w, said amylaceous material
selected from the group consisting of amylose, waxy maize starch, wheat
starch, tapioca starch, pea starch and combinations thereof,
(b) heating said composition to a temperature of no more than about
150.degree. C. at a pressure of no more than about 4000 psi to form a
uniform hot melt from said composition without destructurising said
amylaceous material within said composition, and
(c) forming said hot melt into a desired matrix shape,
incorporating said agriculturally active agent is incorporated in said
composition in steps (a) or (b) or within said matrix shape produced in
step (c),
optionally incorporating within said composition of steps (a) or (b) a
filler in an amount of less than about 95% by weight and a plasticizer in
an amount of up to about 20% by weight, and further optionally
incorporating a synthetic polymer in an amount of up to about 90% by
weight within said composition of steps (a) or (b) or within said matrix
shape produced in step (c).
2. A method according to claim 1 wherein said active agent is incorporated
into said matrix shape by admixing with said composition in step (a).
3. A method according to claim 1 wherein said active agent is admixed with
said hot melt during step (b).
4. A method according to claim 1 wherein the hot melt is formed into said
matrix shape by extrusion.
5. A method according to claim 4 wherein the temperature during extrusion
is in the range of from 70.degree.-100.degree. C. and the pressure is from
200-500 psi.
6. A method according to claim 1 further comprising subjecting the hot melt
to atmospheric or sub-atmospheric pressure immediately prior to or during
step (b) to remove water from the hot melt prior to the formation of the
matrix shape.
7. A method according to claim 6 further comprising the step of
crosslinking the amylaceous material during or after step (b).
8. A method according to claim 1 wherein said amylaceous material is
selected from the group consisting of amylaceous ethers, amylaceous
esters, and combinations thereof, amylaceous alkyl succinates and starch
molecules having synthetic polymeric branches grafted thereon.
9. A method according to claim 8 wherein the amylaceous ether is a
hydroxyalkyl derivative or carboxyalkyl derivative.
10. A method according to claim 9 wherein the amylaceous ester is a
saturated fatty acid derivative.
11. A method according to claim 9 wherein the amylaceous alkyl succinate is
starch octenyl succinate.
12. A method according to claim 1 wherein the composition of step (a)
comprises from about 2% to about 20% by weight of water.
13. A method according to claim 12 wherein the composition of step (a)
comprises from about 5 to about 15% by weight of water.
14. A method according to claim 1 wherein said synthetic polymer is present
in the composition in an amount of less than about 25% by weight.
15. A method according to claim 14 wherein the hot melt is formed into the
desired shape by extrusion at a temperature of from
120.degree.-140.degree. C. and a pressure of from 100-1000 psi.
16. A method according to claim 15 wherein in step (b), the matrix shape is
co-formed with at least one layer of a synthetic polymer.
17. A method according to claim 16 wherein the matrix shape is co-extruded
with the synthetic polymer.
18. A method according to claim 15 wherein the matrix shape from step (b)
is coated with a synthetic polymer by way of spraying or brushing.
19. A method according to claim 14 wherein said synthetic polymer is
present in the composition in an amount of less than about 15% by weight.
20. A method according to claim 1 wherein the synthetic polymer is selected
from the group consisting of low density polyethylene and high density
polyethylene, a copolymer of ethylene vinyl acetate, a copolymer of
ethylene acrylic acid, polyvinyl chloride, polystyrene, chlorinated
polyethylene, a copolymer of ethylene propylene, a copolymer of acrylic
acid, polyvinyl acetals, polyamines and urethanes.
21. A method according to claim 1 wherein the composition comprises a
filler in an amount of less than about 70% by weight of said composition.
22. A method according to claim 21 wherein said filler is selected from the
group consisting of metal salts, clays, carbonaceous material, dextrose,
talcs, silicas and ammonium sulphate.
23. A method according to claim 22 wherein said filler is selected from the
group consisting of calcium carbonate, calcium sulphate, sodium carbonate,
sodium sulphate, barium sulphate, kaolin, bentonite and wood flour.
24. A method according to claim 1 wherein a filler is incorporated into
said composition prior to or during step (b).
25. A method according to claim 1 wherein the composition of step (a) or
step (b) includes a plasticizer selected from the group consisting of a
mono- or polyfunctional alcohol, invert sugar, dioctyl phthalate,
chlorinated hydrocarbons, vegetable oil, and combinations thereof.
26. A method according to claim 25 wherein said alcohol is selected from
the group consisting of polyethylene glycol, acetyl glycol and glycerol.
27. A method according to claim 25 wherein said vegetable oil is soya bean
oil.
28. A method according to claim 1 wherein said active agent is selected
from the group consisting of acaricides, insecticides, nematicides,
herbicides, fungicides, plant growth regulants, fertilizers, trace
nutrients, biological control agents and combinations thereof.
29. A method according to claim 28 wherein said active agent is selected
from the group consisting of chlorpyrifos, carbosulfan, carbofuran,
phorate, diuron and Bacillus thuringiensis.
30. A method according to claim 1 wherein said active agent is blended with
the matrix shape from step (c).
31. A method according to claim 30 wherein said active agent is
incorporated into said matrix shape by immersion or infusion.
32. A method according to claim 30 further comprising the step of cooling
or allowing the matrix shape to cool prior to incorporating said agent
herewith.
33. A controlled release biodegradable composition comprising a matrix of
an amylaceous material in combination with an agriculturally active agent,
said matrix formed by
(a) providing a composition comprising an amylaceous material having an
amylose content of at least 50% w/w and water, said water being present in
an amount of from about 2 to about 30% w/w, said amylaceous material
selected from the group consisting of amylose, waxy maize starch, wheat
starch, tapioca starch, pea starch and combinations thereof,
(b) heating said composition to a temperature of no more than about
150.degree. C. at a pressure of no more than about 4000 psi to form a
uniform hot melt from said composition without destructurising said
amylaceous material, and
(c) forming said hot melt into said matrix,
and said agriculturally active agent subject to controlled release and
selected from the group consisting of acaricides, insecticides,
nematicides, herbicides, fungicides, plant growth regulants, fertilizers,
trace nutrients, biological control agents and combinations thereof, said
matrix optionally comprising up to about 90% by weight of a synthetic
polymer, up to about 20% by weight of a plasticizer and up to about 95% by
weight of a filler.
34. A controlled release biodegradable composition according to claim 33
comprising a matrix comprising less than about 15% by weight of a
synthetic polymer.
35. A controlled release biodegradable composition according to claim 33
wherein the amylaceous material is selected from the group consisting of
amylaceous ethers, amylaceous esters, and combinations thereof; amylaceous
alkyl succinates and starch molecules having a synthetic polymer grafted
thereon.
36. A controlled release biodegradable composition according to claim 35
wherein the amylaceous ether is a hydroxyalkyl derivative or carboxyalkyl
derivative.
37. A controlled release biodegradable composition according to claim 36
wherein said amylaceous ether is a hydroxyethyl, hydroxypropyl,
hydroxybutyl or carboxymethyl derivative.
38. A controlled release biodegradable composition according to claim 35
wherein the amylaceous alkyl succinate is starch octenyl succinate.
39. A controlled release biodegradable composition according to claim 35
wherein the amylaceous ester is a saturated fatty acid derivative.
40. A controlled release biodegradable composition according to claim 35
wherein said amylaceous material is crosslinked.
41. A controlled release biodegradable composition according to claim 33
wherein the synthetic polymer is selected from the group consisting of low
density polyethylene and high density polyethylene, ethylene vinyl acetate
copolymers, ethylene acrylic acid copolymers, polyvinyl chlorides,
polystyrenes, chlorinated polyethylenes, ethylene propylene copolymers,
acrylic acid copolymers, polyvinyl acetals, polyamines and urethanes.
42. A controlled release biodegradable composition according to claim 33
wherein the matrix is coated with the synthetic polymer.
43. A controlled release biodegradable composition according to claim 33
wherein the active agent is selected from the group consisting of
chlorpyrifos, carbosulfan, carbofuran, phorate, diuron and Bacillus
thuringiensis.
44. A controlled release biodegradable composition according to claim 33
wherein the filler is selected from the group consisting of metal salts,
clays, carbonaceous material, dextroses, talcs, silicas and ammonium
sulphate in an amount of less than about 70% by weight.
45. A controlled release biodegradable composition according to claim 44
wherein said filler is selected from the group consisting of calcium
carbonate, calcium sulphate, sodium carbonate, sodium sulphate, barium
sulphate, kaolin, bentonite and wood flour.
46. A controlled release biodegradable composition according to claim 33
having a dermal LD.sub.50 as measured on rabbits which is greater than the
dermal LD.sub.50 for said active agent as measured on rabbits.
47. A controlled release biodegradable composition as claimed in claim 33
which is adapted for application to a crop growing area.
48. A controlled release biodegradable composition according to claim 33
wherein said composition includes a plasticizer selected from the group
consisting of a mono- or polyfunctional alcohol, invert sugar, dioctyl
phthalate, chlorinated hydrocarbons, vegetable oil and combinations
thereof.
49. A controlled release biodegradable composition according to claim 33
wherein said synthetic polymer is present in an amount of up to about 25%
by weight.
Description
TECHNICAL FIELD
This invention relates to a biodegradable or digestible matrix, and more
particularly to a matrix suitable for controlled release of an active
agent into an environment or for controlled rate of biodegradation or
digestion. The invention also relates to a method for manufacture of the
matrix and to use of the matrix in agriculture.
BACKGROUND ART
In agriculture it is desirable to release fertilizers, pesticides,
herbicides or the like active agents to the soil at a controlled rate over
a prolonged period. Depending on the type of active agent and the
agricultural requirement, the period of release may be desirably a period
of weeks, months or years. Furthermore, it is sometimes desirable that the
active agent be released at an initially high rate and then at a slower
rate.
It has been practised to prepare copolymers comprising a synthetic polymer
as the major component with minor amounts of starch as absorbents. These
grafted polymers are used in agriculture for example, as a coating for
seeds. The polymer absorbs water and holds it at the seed surface, thus
increasing both the rate of germination and the percentage of the total
number of planted seeds which germinate. Examples include starch
polyacrylates, starch acrylonitriles, starch polyethylenes, starch-vinyl
copolymers and the like.
Similarly, it is known to manufacture so called biodegradable films from
synthetic polymers for use in for example agriculture as mulch films. Some
of these films include starch as a minor component.
However, in general, the starch-synthetic copolymer compositions and
synthetic films suffer from the disadvantage that they are not truly
biodegradable. Disadvantageously, when the composition disintegrates, the
synthetic organic residue remains as an environmental pollutant.
It has also be practised to encapsulate active agents so that an inner core
of the toxic agent is surrounded by a polymeric matrix. The polymeric
matrix may include starch. These products form a sponge like structure
which holds the active ingredient when dry but releases it upon wetting.
Release is generally effected by the rupture of the enveloping membrane.
Accordingly, although these materials may be fully biodegradable, it is
difficult to control the rate of release and also to control the rate of
degradation. The production of such incorporated agents involves complex
and critical manufacturing steps.
The present invention stems from the surprising and unexpected discovery
that an active ingredient can be controllably released into an environment
at a predetermined rate from a biodegradable matrix based on a starch
derived material and that the release rate of the active ingredient can be
varied independently of the rate of degradation of the matrix.
The biodegradable matrix of the invention has been developed primarily for
use in agriculture and will be described hereinafter with reference to
that application. However, it will be appreciated that the invention is
not limited to that particular field of use.
DISCLOSURE OF THE INVENTION
It is a first object of the present invention to provide a method for the
manufacture of a biodegradable matrix shape having an active agent
incorporated therewith to be controllably released from the matrix into an
environment at a predetermined rate.
It is a second object of the present invention to provide a biodegradable
composition for the controlled release of an active ingredient into an
environment which in preferred embodiments, avoids or at least ameliorates
the above discussed deficiencies of the prior art.
According to one aspect, the invention consists in a method for manufacture
of a controlled release biodegradable matrix shape containing an
agriculturally active agent subject to controlled release, said method
comprising the steps of:
a) heating at a temperature of no more than about 150.degree. C. and
subjecting to a pressure of no more than about 4000 psi a composition
having a water content of from about 2 to about 30% w/w and comprising an
amylaceous material having an amylose content of at least 50% w/w or a
derivative thereof selected or derived from the group consisting of
amylose, maize starch including waxy maize starch, wheat starch, tapioca
starch, pea starch or a combination thereof, and water; so as to provide a
uniform hot melt without destructurising the amylaceous material or
derivative thereof, b) forming the hot melt into a desired matrix shape,
step (a) or step (b) further comprising including a filler in an amount of
less than about 95% by weight, 0 to less than or equal to about 90% by
weight of a synthetic polymer and optionally a plasticizer, if synthetic
polymer is present, in an amount of about 20% by weight or less, and
c) incorporating the agent in the matrix shape, the composition and forming
conditions of the matrix shape being selected so as to provide a
predetermined rate of biodegradation whilst the concentration and type of
filler is selected so as to provide a controlled rate of release of said
agent independent of said rate of biodegradation.
According to a second aspect, the invention consists in a controlled
release biodegradable composition comprising a matrix formed by heating at
a temperature of no more than about 150.degree. C. and subjecting to a
pressure of no more than about 4000 psi, a composition having a water
content of from about 2 to about 30% w/w and comprising an amylaceous
material having an amylose content of at least 50% w/w or a derivative
thereof selected or derived from the group consisting of amylose, maize
starch including waxy maize starch, wheat starch, tapioca starch, pea
starch or a combination thereof, and water; to provide a uniform melt
without destructorising the amylaceous material or derivative thereof;
from 0 to less than or equal to about 25% by weight of a synthetic
polymer; an active agent subject to controlled release and selected from
the group consisting of acaricides, insecticides, nematicides, herbicides,
fungicides, plant growth regulants, fertilizers, trace nutrients,
biological control agents or a combination thereof; from 0 to about 20%
w/w of plasticizer if synthetic polymer is present and a filler in an
amount of less than about 95% by weight, the composition and forming
conditions of the matrix being selected so as to provide a predetermined
rate of biodegradation whilst the concentration and type of filler is
selected so as to provide a controlled rate of release of said agent
independent of said rate of biodegradation.
According to a third aspect, the invention consists in a method of
agriculture which comprises applying to a crop growing area a matrix shape
produced by the method according to the first aspect or the composition
according to the second aspect.
For the purposes of this specification, the term "amylaceous material"
means starch or flour from any cereal crop, root crop, leguminous crop or
any other commercial source of starch and includes for example wheat
starch, maize starch including waxy maize starch, potato starch, tapioca
starch, pea starch or a combination thereof, amylose or amylopectin alone
or any combination of amylose and amylopectin.
A "derivative" of amylaceous material includes modified amylaceous
materials (for example chemically modified amylaceous materials),
amylaceous compositions formed during hot melting or during forming
amylaceous material alone or in combination with plasticizers,
crosslinking agents or the like. The term also includes starch molecules
having a synthetic polymer grafted thereon.
"Synthetic polymer" includes non-naturally occurring polymers such as those
used for plastics and elastomers and the term includes within its scope
both thermoplastic and thermosetting polymers.
The term "forming" in relation to the hot melt includes the formation of
films, rods, strands, sheets, pellets or the like and includes, as the
context admits, extrusion through a die head and in a blow moulding
machine.
The present invention particularly relates to the controlled release of an
active agent selected from the group comprising acaricides, insecticides,
nematicides, herbicides, fungicides, plant growth regulants, fertilizers,
trace nutrients or a combination thereof into an environment. Preferably
the environment is a terrestrial environment and in a highly preferred
embodiment the environment is a crop growing area. However, the invention
will be understood to be suitable for use in aquatic environments.
BRIEF DESCRIPTION OF DRAWINGS
The file of this patent contains at least one drawing executed in color.
Copies of this patent with color drawings will be provided by the Patent
and Trademark Office upon request and payment of the necessary fee.
Preferred embodiments of the invention will now be described, by way of
example only, with reference to the accompanying graphs wherein cumulative
% weight loss is shown on the y axis, time of incorporation in soil (days)
is shown on the x axis, soil temperature is shown in degrees Celsius and
soil moisture represented by the symbols FP, H, M and L wherein FP
represents a flood plot where excess water is present, H represents a high
soil moisture content of from 26% to 40% by weight, M represents a medium
soil moisture content of from 6% to 20% by weight and L represents a low
moisture content of from 3% to 17.6% by weight.
FIGS. 1 to 4 show the effect of soil moisture and soil temperature on the
degradation rate of a biodegradable matrix according to the invention.
FIG. 5 shows the effect on the degradation rate of the addition of a
crosslinking agent to the amylaceous material during or after forming into
a matrix shape.
FIGS. 6 and 7 show the effect of product shape on the degradation rate of
the matrix.
FIGS. 8 to 10 show the effect of the incorporation of synthetic polymers on
the degradation rate of the matrix.
FIGS. 11 and 12 show the effect of the incorporation of fillers on the
degradation rate of the biodegradable matrix.
FIG. 13 shows the variation in the release rate of the active agent that
may be obtained by the selection of either carbosulfan, chlorpyrifos or
phorate.
FIG. 14 shows the effect of the introduction of an active agent on the
degradation rate of the biodegradable matrix.
FIG. 15 shows the release rate of the active agent from those matrices from
FIG. 14 including an active agent.
FIG. 16 shows the effect of the addition of 9% filler ›(NH.sub.4).sub.2
SO.sub.4 ! on the release rate of the active agent.
FIGS. 17 to 48 show release and degradation rates of a biodegradable matrix
according to the invention.
FIGS. 49 to 68 are scanning electron photomicrographs of biodegradable
matrices according to the present invention.
BEST MODES FOR CARRYING OUT INVENTION
The biodegradable composition according to the invention is desirably
formed from a "hot melt" process.
In preferred embodiments of the method for manufacture according to the
invention, a composition comprising an amylaceous material or a derivative
thereof is first prepared by mixing an amylaceous material and an amount
of water in sufficient proportion to form a free-flowing powder.
In preferred embodiments of the invention, the amylaceous material used is
high amylose maize starch comprising at least 50% by weight of amylose or
a modified derivative of this starch.
Where a high amylose maize starch is used, it is desirable to select a high
amylose maize starch or modified starch derived from the Goodman Fielder
Mills Pty Ltd maize hybrids 55/77 or 65/88 described in detail in the
applicant's co-pending application No. PCT/AU90/00237 incorporated herein
by cross-reference.
By modifying the basic starch, it is possible to confer different
properties on the final matrix shape. A large number of derivatives of
amylaceous materials are suitable for use in the present invention. These
include
(i) ether derivatives such as
a) hydroxyalkyl derivatives, for example hydroxyethyl, hydroxypropyl and
hydroxybutyl and
b) carboxyalkyl derivatives, for example carboxymethyl, and
ii) ester derivatives such as saturated fatty acid derivatives, for example
acetyl and succenyl. Mixed derivatives are also suitable for use in the
present invention.
In addition, the ether and ester derivatives may be crosslinked such as for
example, distarch phosphate or distarch glycerol. In such case,
modification may be achieved by using a crosslinking agent such as sodium
trimetaphosphate. Cross bonded high amylose maize starch and cross bonded
common wheat starch are particularly suitable modifications for use in the
present invention. The amylaceous material may be precrosslinked, that is
be crosslinked prior to or during conversion to the hot melt. However,
preferably, the amylaceous material is crosslinked during forming and more
preferably after forming by any suitable method readily understood by
those skilled in the art. For example, in one embodiment the matrix shape
is extruded into a bath comprising the crosslinking agent, saturation
allowed to take place and the matrix removed and allowed to dry and cure.
Derivatives which confer various degrees of hydrophobicity to the finished
composition are particularly desirable. Such derivatives include
amylaceous alkylsuccinates and in particular, starch octenyl succinate and
starch molecules having synthetic polymeric branches grafted thereon.
However, carboxymethylated, hydroxypropylated and acetylated high amylose
modified maize starch derivatives are preferred.
By selecting the starch modification, the mechanical properties of the
matrix shape may be varied. For example, the selection of an acetylated
high amylose starch having an acetyl value of about 2.5% or a
hydroxypropylated high amylose starch having a hydroxypropyl value of up
to about 3% allows higher processing temperatures to be utilized thereby
resulting in films having improved handling characteristics in that the
hot melt is less fluid and more rubbery in nature. Carboxymethylated
starch derivatives having a carboxyl value of about 2% are also
particularly suitable for use in the present invention.
The nature of the crosslinking agent and the stage at which the
crosslinking agent is incorporated into the amylaceous material affects
such physical properties of the matrix shape as biodegradability, release
rate, flexibility, strength, surface finish and colour.
For a uniform hot melt phase to form, it is believed necessary that an
amount of water be present in the composition used to form the hot melt.
Preferably, the composition contains water in less than the minimum amount
required to dissolve all the amylaceous solid material, that is the
composition contains less than about 50% by weight of water. More
preferably, the composition comprises from about 2% to about 30% by weight
of water. However, the minimum amount of water required to form a uniform
hot melt may be employed. Accordingly, the amount of water may vary down
to a few percent. It is emphasised that these amounts represent the total
amount of water in the composition used to form the hot melt and not the
amount of added water. In fact, amylaceous material as normally dried in
preparation typically comprises from 9 to 20% by weight of water and as
such, the residual moisture inherent in the amylaceous material may be
sufficient to enable the conversion of the composition into a hot melt and
additional water need not be added or be added in small quantities only.
However, preferably, water is added in an amount of less than 50% by
weight, more preferably less than 20% by weight and most preferably from
about 5% to about 15% by weight.
The amount of water may be selected so as to modify the physical properties
of the final product. For example, the higher the water content, the
higher the flexibility and the lower the strand strength of the matrix
shape.
In addition to the amylaceous material and water, the composition for
preparing the hot melt may also include optional ingredients such as
synthetic polymers, fillers, plasticizers, weighting agents, U.V.
stabilizers, pore structure modifiers and the like.
The applicant has discovered that the addition of synthetic polymers during
the preparation of the biodegradable matrix shape affects both the
performance and processing of the matrix. Preferably, the synthetic
polymer is added to the composition before processing to a hot melt,
although it may be added during the conversion or be applied to the matrix
shape itself during forming by way of co-forming or alternatively, the
matrix shape may be coated immediately after forming, for example by way
of spraying, brushing or dipping. The co-forming technique employed may be
any one of those currently used in the plastic industry, for example
thermal lamination, co-injection or co-extrusion using the cast (flat die)
method or strand die method or in blown film production.
The applicant has discovered that the inclusion of a synthetic polymer in
the biodegradable matrix shape results in a more absorbent product for
some active agents and a matrix shape having a greater shelf life
stability. Further, the applicant has made the surprising and unexpected
discovery that where an ethylene vinyl acetate starch copolymer is used, a
two phase system forms in the cooled matrix. The presence of these two
apparently continuous phases of starch and synthetic polymer results in a
very high surface area honeycomb of the ethylene vinyl acetate phase once
the starch phase has degraded. Further, the phase separation/compatibility
may be adjusted by modifying the side chain components of the modified
starches.
The synthetic polymer may be added in an amount of up to about 90% by
weight of the composition, hot melt or the matrix shape respectively.
However, preferably, no more than about 25% by weight and more preferably
less than or equal to about 15% by weight synthetic polymer is added since
in general, the larger the synthetic polymer component, the slower the
degradation rate of the matrix shape.
The synthetic polymer may be any conventional thermoplastic or
thermosetting polymer but is preferably selected from the group consisting
of polyethylene (including low density polyethylene, linear low density
polyethylene and high density polyethylene), ethylene vinyl acetate
copolymers, ethylene acrylic acid copolymers, polyvinyl chlorides,
polystyrenes, chlorinated polyethylenes, ethylene propylene copolymers,
acrylic acid copolymers, polyvinyl acetals copolymers, polyamines,
polyethylene terephthalates, phenolic resins and urethanes. Most
preferably, the synthetic polymer is thermoplastic and is low density
polyethylene, linear low density polyethylene, or high density
polyethylene; an ethylene vinyl acetate copolymer having a vinyl acetate
content of from 5% to 40% W/W and melt flow index of from 0.5 to 400 g/10
minute as determined by the ASTM test D1238; or polyvinyl chloride or
chlorinated polyethylene having a chlorine content of from 20% to 50% W/W.
The synthetic polymer may be selected to modify or decrease both the
biodegradation rate of the matrix shape and the release rate of the active
agent. Further, the applicant has found that the addition of a synthetic
polymer to the matrix affects the mechanical properties of the finished
article. For instance, at the 10% addition level both chlorinated
polyethylene and polyvinyl chloride increase strand strength and
flexibility of the final matrix shape. Conversely, at the 10% addition
level, ethylene vinyl acetate copolymers decrease strand strength yet
increase flexibility. Both strand strength and flexibility are
advantageous for the purposes of handling and storage of the finished
product as matrices exhibiting these properties tend to retain their shape
and integrity.
The addition of non polymeric fillers also serves to modify processing and
performance characteristics of the hot melt and final product. Fillers may
be added to the composition prior to conversion into the hot melt or be
added to the hot melt prior to formation of the matrix shape. Water
soluble, water insoluble, organic, inorganic, ionic and non-ionic fillers
are suitable for use in the present invention. Preferably, the selected
filler is non-toxic to the environment. Specific examples of suitable
fillers include metal salts, clays, carbonaceous materials, dextrose,
talc, silicas and ammonium sulphate. Preferably, the metal salt is calcium
carbonate, calcium sulphate, sodium carbonate, sodium sulphate or barium
sulphate, the clay kaolin or bentonite and the carbonaceous material wood
flour. The fillers may be included in the formulation at levels up to
about 70% by weight. However, formulations comprising up to about 95% by
weight non polymeric filler are also envisaged by the present invention.
The addition of plasticizers and lubricants improves both the extrusion
characteristics of the hot melt and the physical properties of the matrix
shape. The plasticizer may be added to the composition prior to conversion
into the hot melt or to the hot melt prior to formation. Generally, any
known plasticizer can be utilized in the present invention. However,
specific examples of suitable plasticizers include mono or polyfunctional
alcohols. Polyethylene glycol, acetyl glycol, glycerol, invert sugar,
dioctyl phthalate, vegetable oils (preferably soya bean oil), chlorinated
hydrocarbons and combinations thereof are preferred.
The amount of plasticizer to be used will vary up to about 20% by weight of
the formulation. However, the presence of an auxiliary plasticizer is not
essential.
In order for the hot melt to form, the amylaceous containing composition
must be subjected to elevated temperatures and pressure. The temperatures
best suited for this conversion are from about 70.degree. C. to about
150.degree. C. depending on the formulation. Where the matrix shape is
formed without vacuum venting in an extruder, the preferred temperatures
are as set out below.
__________________________________________________________________________
WITH SYNTHETIC
POLYMER
WITHOUT SYNTHETIC POLYMER
Underwater pelletising
Strand Pelletising
EXTRUDER
Temperature (.degree.C.)
Temperature(.degree.C.)
__________________________________________________________________________
Zone -
1 70-80 120-135 120-135
2 70-80 120-135 130-135
3 70-85 125-135 130-135
4 75-85 130-138 135-140
5 80-85 130-140 135-140
6 85-90 130-140 135-140
Melt Pump
Zone -
7 85-90 130-140 --
8 85-90 130-140 --
9 85-90 130-140 --
Melt Filtration
Zone
10 85-90 130-140 --
11 85-90 130-140 --
12 85-90 130-140 --
Die Transition
85-95 130-140 --
Die Plate
85-95 130-140 140-145
__________________________________________________________________________
However, where the active agent has been incorporated before or during
processing, the conversion and forming steps respectively are preferably
performed below the temperature at which the active agent breaks down.
Where the active agent is incorporated with the matrix shape after
forming, higher processing temperatures may be used providing the matrix
shape is cooled or allowed to cool prior to incorporating the active agent
therewith.
The pressure for conversion of the amylaceous containing composition to a
hot melt is about 200 psi to about 4000 psi, preferably as set out below.
__________________________________________________________________________
WITH SYNTHETIC POLYMER
WITHOUT SYNTHETIC POLYMER
PRESSURE (psi)
PRESSURE (psi) Underwater pelletising
Strand Pelletising
__________________________________________________________________________
EXTRUDER 200-500 1000-2000 100-1000
MELT PUMP OUTLET
1500-2500 1500-2500 --
DIE TRANSITION
1500-2500 1500-2000 --
__________________________________________________________________________
In one embodiment, the hot melt is subjected to a reduced pressure
immediately prior to the forming step to remove water and other volatiles
from the hot melt. This step is especially desirable where the melt is to
be extruded as a film. Desirably, the reduced pressure is in the form of a
vacuum stripping step at a pressure of for example less than 200 mbar.
Alternatively, the hot melt is subjected to a series of reduced pressures
prior to the forming step to sequentially remove a potion of the water and
other volatiles from the hot melt at each venting step.
The hot melt is then formed into the desired matrix shape by any
conventional process such as dies or rolls into any desired size or shape
including pellets, chips, ribbons, films and the like.
In another embodiment of the invention, the matrix obtained from the
process described hitherto and an amount of water sufficient to form a
uniform hot melt is subsequently subjected to elevated temperatures and
pressures for conversion into a second hot melt which can be shaped or
moulded by any conventional process into the desired shape and size as
described above.
If desired, some or all of the optional ingredients such as synthetic
polymers, fillers, plasticizers and the like hitherto described may be
added before, during or after this second processing step in accordance
with the teachings set forth above.
The active agent may be added in powder or liquid form as part of the
formulation before conversion to either the first or second hot melt,
during either conversion or be incorporated with either the first or
second matrix shape during or after forming for example, by way of
immersion or infusion. Preferably, the active agent is incorporated during
the final forming step when the active ingredient may be intimately mixed
with the hot melt.
The active agent is preferably selected from the group comprising
acaricides, insecticides, nematicides, herbicides, trace nutrients, plant
growth regulants, fertilizers, fungicides, microorganisms for biological
control or the like, or combinations thereof.
Representative examples of acaricides, insecticides and nematicides known
to those skilled in the art include the following available chemicals,
expressed by common name: cadusafos, carbofuran, carbosulfan,
chlorfenvinphos, chlormephos, chlorpyrifos, chlorpyrifos-methyl,
cloethocarb, cyhalothrin, deltamethrin, alphamethrin, dicrotophos,
disulfoton, endosulfan, ethiofencarb, ethoprophos, fenamiphos,
fensulfothion fonofos, furathiocarb, isazofos, methomyl, monocrotophos,
oxamyl, parathion-methyl, parathion, phorate, pirimicarb, pirimiphos
ethyl, pirimiphos methyl, quinalphos, tefluthrin, temephos, terbufos.
Herbicides to be used in the composition of the present invention depend on
the plant desired to be destroyed. Therefore, the class of herbicides
known to those skilled in the art for destroying undesirable plants are
active agents within the concept of the present invention. Representative
examples of herbicides, expressed by common name, include the following:
ametryn, amitrole, atrazine, bromoxynil, chlorsulfuron, cyanazine, 2,4-D
and related compounds, desmethryn, di-allate, diquat, diuron, EPTC
glyphosate linuron, MCPA and derivatives, metolachlor, metribuzin,
paraquat, pendimethalin, picloram, simazine, terbutryn, triallate,
triclopyr, trifluralin.
Similarly, the fungicides to be used in the composition of the present
invention depends upon the fungi desired to be destroyed. Representative
examples of fungicides known to those skilled in the art and suitable for
use in the present invention include the following expressed by common
name: benalaxyl, benomyl, chlorothalonil, etridiazole, fosetyl, phosphoric
acid and its salts and derivatives, imazalil, metalaxyl, pyrazophos,
quintozene, triadimefon.
Specific examples of plant growth regulants, that is compounds especially
formulated to make a specific portion of the plant grow faster than
others, and other compounds suitable for incorporation with the matrix
shape include: chlormequat, nitrapyrin, paclobutrazol, urea, monoammonium
phosphate, diammonium phosphate, chelated trace elements, trace nutrients,
potassium sulphate, ammonium sulphate, potassium ammonium sulphates.
Suitable trace nutrients include those compounds recognised as essential or
desirable for healthy plant growth and include amongst others, oxides and
salts of trace elements utilized by plants.
Suitable microorganisms for biological control include Bacillus
thuringiensis.
The nature of the active agent may be selected on the basis of the desired
release rate of the final biodegradable composition.
The biodegradable compositions according to the invention comprise a matrix
including an amylaceous material or derivative thereof, from 0 to less
than or equal to about 25% by weight of a synthetic polymer and an active
agent intended to be released into an environment at a predetermined rate.
Preferably, the matrix comprises less than or equal to about 15% by weight
synthetic polymer.
Desirably, the matrix is formed from an amylaceous hot melt and more
desirably, by the method described above. The amylaceous material or
derivative thereof and synthetic polymer may be any one of the products
already described. Additionally, the matrix may include other optional
ingredients such as fillers, plasticizers, weighting agents, U.V.
stabilizers, pore structure modifiers and the like, the nature of which
has been discussed previously.
Preferably, the final matrix includes water in an amount of from about 1%
to about 50% by weight and more preferably, from about 2% to about 30% by
weight.
The biodegradable matrix shapes and compositions according to the invention
are particularly suitable for use in agriculture where they are applied
for example, as pellets or ribbons to a crop growing area to improve plant
growth and yield over an extended period of time. The matrix shapes and
compositions may be applied on top of the soil but desirably, they are
applied within the soil. They may be applied to the crop growing area by
any conventional means including ploughing, tilling, banding, cultivating,
furrowing and the like.
The release of the active agent from the biodegradable matrix is thought to
be effected by two main mechanisms, diffusion through the matrix and by
leaching through pores either inherent in the matrix or induced by the
leaching out of soluble salts during service. Further, as the matrix is
itself degrading during service, variations in the matrix surface area
exposed to the environment also affects the rate of release indirectly so
the release rate of the active agent may be controlled to an extent by
controlling the rate of biodegradation of the matrix.
As illustrated by the following examples, and with reference to FIGS. 1 to
16, it is possible to select both the release rate and biodegradation rate
of the matrix shape by the selection of starch type, additives to be
incorporated into the matrix, active agent type and processing conditions.
The formulations represented by FIGS. 1 to 16 are depicted in the following
table.
TABLE 1
__________________________________________________________________________
% W/W OF
FORMULATION
1A 1B 2A 2B 3A 3B 3C 4A 4B 5A 5B 6A 6B 7A 7B 8A 8B 8C
__________________________________________________________________________
A877.sup.1
63.0 72.1
72.1 56.6
56.6
56.6
56.6 72.1
63.0
31.4
Gelose 50.sup.2
62.0 52.8
52.8
52.8
62.0
62.0
Gelose 22.sup.3
64.7
64.7
H.sub.2 O
15.6
30.0
16.1
16.1
25.5
25.5
25.5
30.0
30.0
13.5
9.9
9.9
9.9
14.4
14.4
16.1
15.6
7.8
Glycerol
11.4
8.0
11.8
11.8
6.8
6.8
6.8
8.0
8.0
10.8
10.8
10.8
10.8
10.6
10.6
11.8
11.4
5.7
Dextrose
10.0
Omyacarb 10.sup.4
BaSO.sub.4
(NH.sub.4).sub.2 SO.sub.4
Kaolin
EVA.sup.5 14.9
14.9
14.9 10.0
55.1
Sodium Trimeta 3.6
3.6
3.6
Phosphate
NaHCO.sub.3 9.0
9.0
9.0
9.0
Active Agent
1.sup.6 10.1
10.1
10.1
10.1
10.3
10.3
2.sup.7
3.sup.8
CPE.sup.9
__________________________________________________________________________
% W/W OF
FORMULATION
8D 9A 9B 9C 9D 10A
10B
11A
11B
11C
11D
11E
13A
13B
13C
14A
14B
14C
__________________________________________________________________________
A877.sup.1
7.8
72.1
63.0
31.4
7.8
63.0
63.0
72.1
63.0
63.0
63.0
63.0
47.9
52.8
47.3
Gelose 50.sup.2
Gelose 22.sup.3 64.7
63.8
64.5
23.1
25.5
22.8
H.sub.2 O
2.0
16.1
15.6
7.8
2.0
17.6
17.6
16.1
15.6
15.6
15.6
15.6
14.4
14.2
14.4
6.2
6.8
6.1
Glycerol
1.4
11.8
11.4
5.7
1.4
9.4
9.4
11.8
11.4
11.4
11.4
11.4
10.6
10.4
10.5
Dextrose
Omyacarb 10.sup.4 10.0
BaSO.sub.4 10.0
(NH.sub.4).sub.2 SO.sub.4 10.0
Kaolin 10.0
13.5
14.9
13.4
EVA.sup.5
88.8 10.0
55.1
88.8
Sodium Trimeta
Phosphate
NaHCO.sub.3
Active Agent
9.3
1.sup.6 10.3 10.4
2.sup.7 11.6
3.sup.8 10.6
CPE.sup.9 10.0
10.0
__________________________________________________________________________
% W/W OF
FORMULATION
15A
15B
16A
16B
__________________________________________________________________________
A877.sup.1
Gelose 50.sup.2
47.9
47.3
Gelose 22.sup.3
63.8
55.7
H.sub.2 O
23.1
22.8
14.2
13.8
Glycerol
6.2
6.1
10.4
10.1
Dextrose
Omyacarb 10.sup.4
BaSO.sub.4
(NH.sub.4).sub.2 SO.sub.4
8.8
Kaolin
EVA.sup.5
13.5
13.4
Sodium Trimeta
Phosphate
NaHCO.sub.3
Active Agent
1.sup.6 9.3
2.sup.7 10.4
11.6
11.6
3.sup.8
CPE.sup.9
__________________________________________________________________________
.sup.1 A877 Acetylated high amylose maize starch.
.sup.2 Gelose 50 High amylose maize starch.
.sup.3 Gelose 22 hydroxypropylated high amylose maize starch.
.sup.4 Omyacarb 10 One grade of CaCO.sub.3 (filler).
.sup.5 EVA Ethylene vinyl acetate copolymer (20% vinyl acetate content).
.sup.6 Chlorpyrifos.
.sup.7 Carbosulfan.
.sup.8 Phorate.
.sup.9 Chlorinated Polyethylene (36% Cl Content).
All formulations in Table 1 were preblended for 10 minutes at ambient
temperature in a high speed Prodex blender to form a free flowing uniform
mixture. The blend was then extruded using a Betol BTS 40L twin screw,
co-rotating, intermeshing extruder having six barrel segments each with
separate heating and cooling supply and a die containing an additional two
heating zones. The extruder screws were of constant root diameter with a
constant diameter ratio of 25:1.
All formulations were cooled in air to form strands and pelletized in a
rotary pelletizer (Cumberland manufacture) to form the desired size
pellets in a continuous process. The formulations were extruded under the
following conditions:
Screw speed: 160 rpm
Feed rate: 15 kg/hr
Extrusion temperature: 75.degree.-90.degree. C.
Extruder motorload: 7-12 amps
Extrusion pressure: 600-850 psi.
The initial moisture content and active agent content of each matrix was
determined and the matrix sample incorporated in soil. Said samples were
analysed at periodic intervals for weight loss and active agent loss.
Degradation of the samples were calculated as follows:
##EQU1##
Release rates were calculated as follows:
##EQU2##
FIGS. 1 to 4 show the variation in the degradation rate of typical matrix
formulations as a function of soil moisture and temperature.
From the results obtained, it is evident that the release rates and
biodegradation rates of the matrices according to the invention are
affected by both their solubility in water and soil temperature.
FIG. 1 shows the large difference in degradation rate and total weight loss
obtainable over a period of 168 days for two formulations 1A and 1B under
vastly different soil conditions, that is in a flood plot at 30.degree. C.
and a low moisture soil at 15.degree. C. FIGS. 2 and 3 show typical
degradation rates and total weight losses exhibited by a third formulation
under flood plot (2A) and medium moisture conditions (2B) at a constant
temperature of 30.degree. C. over a period of 35 days. FIG. 3 compares the
degradation rates and total weight losses exhibited by a fourth
formulation over 168 days at 30.degree. C. in high (3A), medium (3B) and
low (3C) soil moisture conditions. FIG. 4 compares the degradation rates
and total weight losses exhibited by the formulation shown in FIG. 1 as 1B
at two soil temperatures ›30.degree. C. (4A) and 15.degree. C. (4B)! but
under constant soil moisture conditions. From these results it is evident
that the higher the soil temperature and moisture content, the greater the
amount and the faster the rate of degradation of the matrix over the
specified time period.
Nevertheless, by modifying the solubility of the matrix it is possible to
alter both the release rate of the active agent and the degradation rate
of the matrix independently of soil conditions. For example, the release
rate may be reduced by the selection of specific starch modifications
which alter the hydrophobicity of the starch thereby preventing or
deterring the dissolution of the starch matrices in wet environments or by
modifying the starch by the introduction of active groups onto the starch
chains which interact with the active agent thereby slowing down the leach
out rate.
Conversely, the selection of a modified starch having reduced chain lengths
induced, for example, by acid or enzyme modification, will result in a
matrix exhibiting an increased rate of release.
The selection of a precrosslinked amylaceous material for subsequent
conversion to the hot melt yields, after forming, a matrix shape which
exhibits a relatively fast rate of release and degradation. This is
somewhat surprising because crosslinked starches are typically more
resistant to degradation and it is believed that this property is
adversely affected by the forming step of extrusion. Conversely, where the
amylaceous material is crosslinked during or after the forming step, the
resulting matrix shape exhibits a slower rate of release and degradation.
It is believed that this change in degradation and release rate is
attributable to formation of an internally crosslinked continuous phase
when the amylaceous material is crosslinked during or after forming and
that this continuous phase is less susceptible to degradation. Conversely,
it is thought that the use of a precrosslinked amylaceous material results
in a matrix shape having a series of crosslinked phases which are more
susceptible to degradation.
FIG. 5 shows the effect of crosslinking on the degradation rate and total
weight loss exhibited by two matrices over a period of 14 days at a
constant soil temperature (30.degree. C.) and moisture condition (medium).
The amylaceous material of matrix 5A is not crosslinked whereas the
amylaceous material 5B was crosslinked after extrusion by the addition of
sodium trimetaphosphate. From this Figure it is evident that the
degradation rate of a matrix may be reduced by the addition of a
crosslinking agent after extrusion.
The selection of certain processing conditions will also affect the
properties of the amylaceous material and therefore, the release rate of
the active agent. For example, by increasing the rate of shear during
processing, the resulting biodegradable matrix will have shorter chains, a
more degraded structure and will therefore release the incorporated active
agent at a faster rate.
The shape of the matrix will affect its degradation rate and therefore, to
an extent, the release rate of the active agent therefrom as shown by
FIGS. 6 and 7 wherein matrix shapes 6A and 7A have a larger surface area
than matrix shapes 6B and 7B respectively. From these Figures it is
evident that the larger the surface area to volume ratio of the matrix
shape, the greater the degradation rate over the specified time period.
The incorporation of a synthetic polymer with the amylaceous material or
matrix shape affects both the release rate and biodegradation rate of the
matrix. It is thought that the synthetic polymers affect the
intermolecular voids in the matrix and thereby, the rate of diffusion and
leaching out of the active agent. It is also thought that they affect the
mechanical properties of the starch molecules thereby affecting the
strength and solubility of the matrix shape.
FIGS. 8 and 9 show the effect of increasing proportions of synthetic
polymers on the degradation rate and total weight loss of four matrices in
two soil moisture regimes, flood plot (FP) and high (H) at a constant soil
temperature of 30.degree. C. The results show little difference in the
overall weight loss between the samples having 0 and 10% ethylene vinyl
acetate respectively, but significant differences are apparent in both the
rate of degradation and total weight loss exhibited by those matrices
having higher amounts of ethylene vinyl acetate.
FIG. 10 shows that there is not necessarily a detectable residue from a
matrix having 10% synthetic polymer (chlorinated polyethlene) incorporated
therein.
The nature and amount of filler may be used to control release rates. Where
a water soluble filler is incorporated with the matrix, upon contact with
moisture, the filler will dissolve over time, thereby creating a series of
pores through which the active agent is actually released. Conversely, the
incorporation of less soluble or insoluble inert fillers with the matrix
reduces the release rate as the starch and active agent is "protected"
from exposure to the environment and consequent dissolution.
FIG. 11 shows the effect of the addition of a variety of fillers on the
degradation rate and total weight loss of a matrix, other factors being
constant.
The rate of degradation and total weight loss of the matrices of FIG. 11 as
a function of soil moisture is illustrated in the family of curves of FIG.
12 wherein,
a) the region between lines 12A and 12B represents the degradation rates
and total weight losses of the matrices of FIG. 11, but excluding the
formulation 11C. comprising 10% (NH.sub.4).sub.2 SO.sub.4, under medium
(M) soil moisture conditions at a soil temperature of 30.degree. C.;
b) the region between lines 12C and 12D represents the degradation rates
and total weight losses of the matrices of FIG. 11 under high (H) soil
moisture conditions at a soil temperature of 30.degree. C.; and
c) the region between lines 12E and 12F represents the degradation rates
and total weight losses of the matrices of FIG. 11 under flood plot (FP)
conditions at a soil temperature of 30.degree. C.
From the Figures it is evident that with the exception of the formulation
comprising 10% (NH.sub.4).sub.2 SO.sub.4, both the amount and rate of
degradation and total weight loss observed for each formulation were
substantially the same, regardless of the level of soil moisture present.
However, the weight loss exhibited by the formulation comprising
(NH.sub.4).sub.2 SO.sub.4 suggests that degradation was not just a result
of dissolution of this water soluble filler.
The nature of the active agent will affect its rate of release. This is
because different active agents will release at different rates under the
same conditions, depending upon their water solubility, partition
coefficients, cohesive energy densities, molecular size and other physical
and chemical properties. FIG. 13 shows the variation in release rates
obtained where three different active agents were compared.
FIGS. 14 and 15 show that the release rate of any active agent is
substantially independent of the biodegradation rate of the matrix. FIG.
14 shows the cumulative % weight loss of three matrices whereas FIG. 15
shows the cumulative % weight loss of the respective active agents from
the corresponding matrices shown in FIG. 14 under the same conditions.
In any event, the release rate of a given active agent may be varied by the
selection of different amounts of the agent or the inclusion in the
formulation of release rate modifiers such as fillers, synthetic polymers
and the like. FIG. 16 illustrates a modification to the release rate that
may be achieved by comparing the total % weight loss of an active agent
from a matrix comprising about 9% w/w ammonium sulphate (16B) with the
total % weight loss of the same active agent from a similar matrix (16A).
That graph clearly shows that incorporation of (NH.sub.4).sub.2 SO.sub.4
in the formulation increased the release rate of the active agent over the
specified time period.
In summary, by selecting the appropriate starting materials and processing
conditions, the release rates and degradation rates of the matrices
according to the invention can be tailored for use in a range of
environments so as to exhibit desired release rates and degradation rates.
The amylaceous material or derivatives thereof used in this invention do
not undergo destructurization during the manufacture of the biodegradable
matrix shapes in which they are incorporated.
This is illustrated in the following experiments.
Experiment 1
Two formulations of the soil insecticide, chlorpyrifos were chosen for this
evaluation. The formulation used is given in Table 2.
TABLE 2
__________________________________________________________________________
Formulation details
Composition
Formul.
Batch
Starch Corvic
No. No. A948
G 50
Glycerol
Water
Attapulgite
6733
Chlorpyrifos
__________________________________________________________________________
G01S05
014241
63.9
-- 4.0 17.3
4.5 -- 10.3
G01S09
024243
-- 60.2
4.0 16.0
4.5 5.0 10.3
__________________________________________________________________________
Starch A948 is sourced from Starch Australasia Ltd as a octenyl succinated
high amylose maize starch, with minimum 80% amylose and succinyl value
2-3.
Starch Gelose 50 (G 50) is sourced from Starch Australasia Ltd as an
unmodified high amylose, with Min. 50% w/w amylose.
Corvic 6733 is sourced from ICI Australia Operations Pty Ltd, as a medium
molecular weight grade polyvinyl chloride, with ISO `K` Value 67, Average
apparent density 530 g/liter, and Total volatile matter less than 0.25%
(Weight reduction, 1 hr/135.degree. C.).
Attapulgite is sourced from Mallina Holdings Ltd, as a Attapulgite grade
080 F, with 85-90 % w/w passing 160 micron, mean particle size 35 micron.
Glycerol is commercial grade glycerol available from a number of sources.
Chlorpyrifos Technical is Dursban FM technical (96% minimum) supplied by
Dow Elenco.
The formulations differ with the incorporation of minor component of a
synthetic polymer (polyvinyl chloride in this case) in one formulation and
the use of chemically modified and unmodified starches. The residual
moisture levels in the starches used in these formulations has been
measured as follows.
______________________________________
A948 12.0% w/w water
G 50 12.5% w/w water
______________________________________
This will give the following moisture levels in the raw material blend feed
to the extruder:
______________________________________
Formulation G01S05 29.3% w/w water
Formulation G01S09 28.5% w/w water
______________________________________
Process description
All the materials (including liquids) used in the formulation were blended
for 10 minutes at ambient temperature in a high speed Prodex blender to
form a free flowing homogeneous powdered mixture.
The blend was then fed to a Betol BTS 40L twin screw co-rotating
intermeshing extruder having six barrel segments, each with separate
electric heater and cooling supply. A die with 2 mm diameter die holes
containing bend electric heater. The extruder screws were of constant root
diameter width a length diameter ratio of 25:1. Both formulations were
cooled in air to form strands and pelletized in a rotary pelletiser
(Cumberland manufacture) form the desired sized pellets, in a continuous
process.
Extrusion conditions
Both formulations were extruded at the same extrusion conditions. The screw
speed was 160 RPM, feed rate 15 kg/hr, extrusion temperatures
75.degree.-90.degree. C, extruder motor load 7-12 AMPS, and extrusion
pressure of 600-850 psi. Detailed extrusion conditions are given in Table
3.
TABLE 3
______________________________________
Extrusion conditions
Formulation
Formulation
Extrusion Parameters
G01S05 G01S09
______________________________________
Extruder Zone 1 75/75 75/76
Zone 2 77/78 77/79
Barrel Zones
Zone 3 80/80 80/81
Temperatures
Zone 4 83/83 83/84
Set/Actual ›.degree.C.!
Zone 5 86/87 86/87
Zone 6 90/91 90/91
Die Temperature Set/Actual ›.degree.C.!
90/90 90/91
Extruder Zone 4 0 0
Vacuum ›-KPa!
Zone 5 0 0
Pressure ›psi!
770 820
Speed ›RPM! 160 160
Load ›AMPS! 7 12
Palletizer Puller 155 155
Cutter 007 007
Pellet size ›L .times. D!
2.0 .times. 1.8
2.0 .times. 1.8
Feed Rate ›kg/hr! 15 15
______________________________________
Release Rate & Degradation testing and Effect of Formulation
The release rate and degradation test were conducted in controlled
environment at temperatures 15.degree. C. and 30.degree. C. and 3 separate
watering regimes to obtain low, medium and high moisture according to the
following technique.
A Technique for Characterising Soil-Applied Controlled
Release Pesticide, Biodegradable Formulations
INTRODUCTION
This method is suitable for testing release of active ingredient and
degradation (weight loss) controlled release (CR) formulations where there
exists a possibility of change of weight during the trial caused by the
following factors:
degradation of matrix
leaching soluble filler from matrix
absorption of water
soil on the surface of recovered granules, and
leaching of plasticiser from the matrix
Formulations where results could be influenced by any of the above factors
should be tested according to this method.
GENERAL DESCRIPTION OF OPERATION
The release rate test station consists of two temperature controlled
environments (30.degree. C., 15.degree. C.) vans. Each temperature
controlled van is divided into 3 separate watering regimes:--Low
(temperate), Medium (subtropical) and High (tropical).
The low watering zone in both temperature environment assimilates 128 mm
rainfall per annum and is operated such that moisture content of soil is
varied from 47% above the field capacity to the wilting point of the soil.
The medium watering zone delivers the equivalent of 510 mm in the
30.degree. C. environment and 255 mm in the 15.degree. C. environment per
annum and operates such that moisture content of the soiled is varied from
67% above the field capacity to 59% below field capacity.
The high watering zone delivers the equivalent of 510 mm in the 30.degree.
C. environment and 255 mm in the 15.degree. C. environment per annum and
operates such that moisture content of the soils varied from 230% above
field capacity to 117% above field capacity.
Environmental conditions are monitored daily: van humidity, soil
temperature, soil moisture, van temperature, irrigation type and date.
SAMPLE PREPARATION
Sample granules need to be sieved to obtain particle size (particle size
distribution) as per specifications of the product. Moisture content to be
adjusted by placing samples in 30.degree. C. van in an open container for
24 hours. Supply laboratory with samples of 0.500 g.+-.0.010 g, three
replicates to obtain day 0 active ingredient content in mgr active
ingredient per sample.
SAMPLE CONTAINER PREPARATION
The K-line sample jars are given four water outlet holes by means of
piercing with the modified soldering iron which is set up in a drill press
unit located in the Strathpine site workshop. The temperature of the
soldering iron is controlled by a potentiostat.
SAMPLE ESTABLISHMENT
1. Insert a glass-wool plug in the base of the sample container
2. Add fifth grams (50 g) of sieved soil
3. Weight 0.500 g.+-.0.010 g of sample granules and sprinkle evenly onto
the soil surface.
4. Add a further fifty grams (50 g) of sieved soil.
5. Place a glass-wool plug on top of the sample jar.
30 samples to be prepared for each regime, and placed into the relevant
region in the release rate test station. Containers are labelled from one
to ten from left to right and details of the formulation are tagged onto
the rack. The details and position of the sample formulation is then
recorded.
SAMPLE RETRIEVAL
At each time point, 3 samples (R1, R2, R3) are removed and placed
separately into the air forced drying oven. The glass wool plugs need to
be removed from the soil surface to allow rapid evaporation and the
samples are dried for 48 hours at 30.degree. C. The sample granules are
then separated from soil by using adequate sieve and brush. (Special note:
It is very important to recover whole sample, every granule).
Adjust moisture content by placing granules in 30.degree. C. van in a open
container for 24 hours, then weigh them and place into labelled sealed
container for laboratory testing.
ANALYTICAL TESTING
Whole sample need to be tested according to test method No. CPSC-29 and
results reported as mg of active ingredient per sample. R1 and R2 samples
to be tested every time and R3 if results of R1-R2=.+-.2 mg.
DEGRADATION TEST
Recovered weight will be compared with established weight i.e. 0.500
g.+-.0.10 g after moisture equilibration.
TREATMENT OF RESULT
Results are calculated to show cumulative % active ingredient released, and
degradation as cumulative weight loss of granules as per formulas:
##EQU3##
Results are represented graphically (FIGS. 17-24) to show percentage of
active released or degradation as a function of time.
Release Rate and Degradation of G01S05 & G01S09
FIGS. 17-20 represent release rate and degradation rate of formulation
G01S05 at temperatures 30.degree. C. and 15.degree. C. respectively.
FIGS. 17 and 18 show significant influence of moisture on release rate and
degradation rate at temperature 30.degree. C.
FIG. 19 shows slight influence moisture on release rate at 15.degree. C.
while degradation is much faster at high (H) moisture then at low (L) and
medium (M) moisture (FIG. 20).
FIGS. 21-24 represent release rate and degradation rate of formulation
G01S09 at temperatures 30.degree. C. and 15.degree. C. respectively.
Release rate FIGS. 27 and 23 show release rate independent of testing
conditions, while degradation depends on moisture and temperature FIGS. 22
and 24
Effect of the starch modification on the release rate and degradation rate
By selecting the starch modification the release rate of active agent and
the degradation rate of the matrix can be varied. This is shown by testing
two biodegradable chlorpyrifos formulations given in Table 4.
TABLE 4
__________________________________________________________________________
Formulation details
Composition
Formul.
Batch
Starch
No. No. A948
HA008
Glycerol
Water
Attapulgite
Chlorpyrifos
__________________________________________________________________________
G01S05
014241
63.9
-- 4.0 17.3
4.5 10.3
G01S08
038241
-- 64.2
4.0 17.0
4.5 10.3
__________________________________________________________________________
G01S05--Octenylsuccinic anhydride modified High Amylose starch based
controlled release formulation.
G01S08--High Amylose starch based controlled release formulation
HA008--High Amylose starch (Min. 80% Amylose)
A 948--Octenylsuccinic Anhydride modified High Amylose (HA008) starch.
FIGS. 25-36 show effect of starch modification on the release rate of
chlorpyrifos and the degradation rate of the matrix.
FIGS. 25, 27, 29, 31, 33 and 35, clearly show that desired release rate of
active agent can be obtained by chemical modification of the starch.
FIGS. 26, 28, 30, 32, 34 and 36 show effect of starch modification on
matrix degradation.
The processing and extrusion conditions for G01S05 014241 are the same as
described above. G01S08 038241 was produced using similar processing
temperatures and conditions.
Effect of the incorporation of synthetic polymer (PVC) on the release rate
of chlorpyrifos and degradation rate of the matrix
The incorporation of synthetic polymers decreases both release rates of the
active agent and degradation rate of the matrix.
This is shown on examples of the High Amylose starch based controlled
release formulation G01S08 and formulation G01S12 where 5% of the starch
is replaced with Corvic 6733 (PVC) as given in Table 5.
TABLE 5
__________________________________________________________________________
Formulation details
Composition
Formul.
Batch
Starch Corvic
No. No. HA008
Glycerol
Water
Attapulgite
6733 Chlorpyrifos
__________________________________________________________________________
G01S08
038241
64.2
4.0 17.0 4.5 -- 10.3
G01S12
038242
60.2
4.0 16.0 4.5 5.0 10.3
__________________________________________________________________________
FIGS. 37-48 show effect of the incorporation of synthetic polymer (PVC) on
the release rate of chlorpyrifos and the degradation rate of the matrix.
FIGS. 37, 39, 41, 43, 45 and 47 show that release rate of active agent can
be modified by incorporation of synthetic polymer.
FIGS. 38, 40, 42, 44, 46 and 48 show effect of synthetic polymer
incorporation on the degradation rate of the matrix.
Scanning Electron Microscopy Evaluation
Scanning electron microscopy (SEM) technique has been used for evaluating
starch and starch-synthetic polymer based controlled release matrixes with
active agent (chlorpyrifos) and without it. Formulations used for this
trials are given in Table 6.
TABLE 6
______________________________________
Formulation details of the pellets used for SEM trials
Composition
Cor-
Formul.
Batch Starch Gly- Atta- vic Chlor-
No. No. G 50 cerol
Water pulgite
6733 pyrifos
______________________________________
G01S01 344141 64.6 8.6 13.0 4.5 -- 9.3
GBAS01 080241 71.2 9.5 14.3 5.0 -- --
G01S09 029241 60.2 4.0 16.0 4.5 5.0 10.3
GBAS09 080249 67.1 4.5 17.8 5.0 5.6 --
______________________________________
G01S01--Controlled release formulation based on Gelose 50 (G 50 High
Amylose corn starch) containing active agent.
GBAS01--Controlled release matrix for formulation G01S01, no active agent.
G01S09--Controlled release formulation based on starch Gelose 50 and
synthetic polymer (PVC) containing active agent.
GBAS09--Controlled release matrix for formulation G01S09, no active agent.
Extrusion conditions were exactly the same for all formulations, details
are given in Table 7.
TABLE 7
______________________________________
Extrusion conditions
Formu- Formu- Formu-
Formu-
Extrusion lation lation lation
lation
Parameters G01S01 GBAS01 G01S09
GBAS09
______________________________________
Zone 1 75/75 75/76 75/76 75/76
Extruder Zone 2 77/78 77/79 77/79 77/79
Barrel Zones
Zone 3 80/80 80/81 80/81 80/82
Temperatures
Zone 4 83/83 83/84 83/84 83/85
Set/Actual ›.degree.C.!
Zone 5 86/87 86/87 86/87 86/89
Zone 6 90/91 90/91 90/91 90/92
Die Temperature
›.degree.C.!
90/90 90/91 90/91 90/91
Set/Actual
Extruder Zone 4 0 0 0 0
Vacuum ›-KPa!
Zone 5 0 0 0 0
Pressure
770 790 820 820
›psi!
Extruder Speed 160 160 160 160
›RPM!
Load 7 8 12 13
›AMPS!
Pelletizer Puller 155 155 155 155
Cutter 007 007 007 007
Pellet size mm 2.0 .times.
2.0 .times.
2.0 .times.
2.0 .times.
›L .times. D! 1.8 1.8 1.8 1.8
______________________________________
The light microscopy and scanning electron microscopy were conducted at the
University of Technology Sydney Australia.
Light Microscopy
Light Microscopy (magnification.times.40) was conducted for all
formulations containing active agent and formulation without it.
As shown in the accompanying photographs PH1 and PH2, all the light
micrographs of pellets displayed the presence of a coherent structure of
the granules. At this level of magnification details of starch structure
is not visible.
Scanning Electron Microscopy
The pellets were freeze dried for 48 hours prior to mounting to remove any
moisture present. This is to insure than after the pellet has been coated
with gold/palladium and introduced into vacuum of the SEM that no moisture
could be released that would damage the surface coating of the pellet.
Pellets of samples G01S01, GBAS01, G01S09 and GBAS09, were examined for the
presence of residual starch granules.
As indicated in SEM photomicrographs, FIGS. 49-52 the nodular and lumpy
structures were clearly and abundantly evident in all samples. See the
table below for the details of the photomicrographs.
______________________________________
FIGURE Sample
No Magnification
No Description
______________________________________
53 1000 -- Starch Gelose 50 (G50)
granules
54 1000 -- Starch Gelose 50 (G50)
granules
55 300 -- PVC granules
56 30 -- PVC granules - particle
size distribution
57 20 -- Chlorpyrifos crystals -
particle size
distribution
58 300 -- Chlorpyrifos crystals
59 20 -- Attapulgite clay -
particle size
distribution
60 300 -- Attapulgite clay - fine
particles
61 1000 344141 Lumpy structure of the
pellet
62 3000 344141 Lumpy Structure of the
pellet
63 600 080241 Lumpy pellet surface
64 1000 080241 Granule cut
longitudinally with a
scalpel
65 1000 029241 PVC fibres on the
pellet surface/lumpy
pellet structure
66 1500 029241 PVC fibres around
starch granules
67 1000 080249 Machine cut surface of
the pellet
68 1000 080249 Edge of the pellet
______________________________________
The size of the globular shapes in the extruded pellets is consistent with
the size of the maize starch granules used in the formulation, indicating
that the original starch granule structure remains evident in controlled
release products produced under the conditions described above. It is
evident that no structural change, i.e. no destructurisation of the starch
occurred.
Field evaluation
Two formulations G01S05 & G01S09 were evaluated in a bioassay trial against
the eastern false wireworm. Formulation G01S905 was also evaluated in a
field trial for the residual control of chironomid larvae (bloodworms) in
establishing rice crops,
Both trials showed excellent performance of starch based control release
formulations.
Microorganisms for biological control may be used as active agents in the
compositions of the invention.
An example of such microorganisms is Bacillus thuringiensis var. kurstake
(Bt). This microorganism does not survive in an infectious form in soil.
As will be shown in the Example described below, incorporation of Bt into
compositions of the invention gives biologically active formulations.
EXAMPLE
Formulations
A series of 9 formulations of Bt technical (as a 10% w/w concentrate) were
prepared as per Table 8. The key points on these formulations were:
All contained 50% w/w of the Bt technical
Starch base was Gelose 22 (Starch Australasia)
All formulations contained glycerine (glycerol) as a plasticizer for the
starch matrix.
Water levels in the formulations varied from 10% w/w to 18.75% w/w on the
prefeed mixture.
Urea was added to some formulations to improve the plasticizing of the
starch matrix.
Calcium stearate was added to 2 formulations to improve the extrusion
properties of the matrix (to act as an internal lubricant).
Processing Conditions
Extruder temperatures were set at 40.degree. C. for zones 1 through to 6 in
the Betol 40L twin screw co-rotating intermeshing extruder. The die
temperature (zone 7) was set at 40.degree. C. or 50.degree. C. for the
extrusion runs.
Evaluation
The products were evaluated for physical strength and
- Melt Spore
Batch Ca Bt TEMPERATURES pressure count/
No. Gelose 22 Water Glycerine Urea Stearate Technical Zone 1 Zone 2
Zone 3 Zone 4 Zone 5 Zone 6 Zone 7 (die) (psi) gram Comments
041341 44.80 12.50 5.00 0.50 50.00 Set point 40 40 40 40 40 40 40
Coud not extrude. Hi-pressure trips.
Actual 40 43 49 48 46 45 44
042341 44.80 18.75 7.50 0.50 50.00 Set point 40 40 40 40 40 40 40
Pelletized after extrusion completed.
Actual 40 55 48 47 56 51 45 Reasonable cut.
042342 42.80 12.50 5.00 0.50 2.00 50.00 Set point 40 40 40 40 40 40 40
Coud not extrude. Hi-pressure trips.
Actual Worse than 041341.
042343 42.80 18.75 7.50 0.50 2.00 50.00 Set point 40 40 40 40 40 40 40
Coud not extrude. Hi-pressure trips.
Actual
043341 44.00 18.75 7.50 1.00 50.00 Set point 40 40 40 40 40 40 40 1100
3.0 .times.
10(8) Strands very soft. Strands cooled Actual No
recording 30 mins. Pelletized without deformation
and with consistent length.
043342 45.00 18.75 7.50 50.00 Set point 40 40 40 40 40 40 50 1000 1.8
.times.
10(7) Could be pelletized as produced,
Actual 40 55 49 49 55 52 49 lacking strand strength.
043343 40.00 13.75 12.50 50.00 Set point 40 40 40 40 40 40 50 Die
heater failure
Actual 39 40 40 40 42 41 37
049341 40.00 13.75 12.50 50.00 Set point 40 40 40 40 40 40 50 1100
3.0 .times.
10(8) Strands soft and insufficient strength to
Actual 40 55 48 49 57 52 52 cut hot.
050341 40.00 10.00 12.50 50.00 Set point 40 40 40 40 40 40 50
1060-1130 4.2 .times. 10(6) Strand strength slightly better than
Actual 40-41 58-60 50-49 51-53 60-66 54-57 50-50
049341. But not sufficient to cut hot.
050342 44.50 18.75 7.50 0.50 50.00 Set point 40 40 40 40 40 40 50 980
Strand strength and hardness better
Actual 41 56 49 49 57 51 50 than 050341. But still not
sufficient.
More visible porosity in granules cut cold.
Water contents used in formulation calculations
Bt Technical: 6%
Gelose 22: 12% (assumption based on experience)
Product: 6% (Assumption based on experience 24 hrs storage in open
container @ 30 C.
Extrusion
1 kg. batches
10 kg/hr
single strand die
Spore count Bt Tech 2 .times. 10(10)/gram
compatibility with the processing equipment as measured by the ability to
draw strands and to successfully cut the product in a rotating pelletizer.
Several extruded formulations were tested for the ability of the organism
to form spores by measuring the number of viable spores in the formulated
(extruded) product.
Results
The results from these trials are summarised in Table 8. The key findings
are:
The starch matrix incorporating a biological active ingredient can be
successfully extruded to form a uniform starch extruded granule.
The Bt can survive the extrusion temperature required to form a uniform
granule leaving sufficient live spores to potentially act in soil against
pests. There appears to be some correlation of higher extrusion
temperatures with low viable spore number. (see batch No. 050342).
No live spores were found on the outside of the granules. This technique of
incorporating Bt into a starch matrix using very low extrusion temperature
shows promise for the development of "protected" Bt formulation which may
remain active in soil for control of soil pests.
It will be apparent that the biodegradable composition according to the
present invention offers the following advantages:
(a) the biodegradable composition provides for the controlled release of an
active agent therefrom into an environment over a prolonged period as
required;
(b) the biodegradable composition may be tailored to exhibit a variety of
release and degradation rates in a range of environments;
(c) as apparent from the Figures, where desired, the active agent can be
released at an initially high rate and then at a slower rate as required;
(d) the matrix is biodegradable and over a period of time will break down
in an environment.
Further, the use of the biodegradable matrices in compositions according to
the invention is advantageous in that they exhibit reduced toxicity
behaviour when compared with the toxicity of the active agent used alone
or in conventional synthetic polymeric formulations as evident from the
following dermal toxicity test carried out with moistened product in
accordance with the United States Environmental Protection Agency data
generation guidelines.
In this regard, phorate was incorporated in a biodegradable matrix in
accordance with the formulation shown below in Table 9:
TABLE 9
______________________________________
TEST
Ingredient Percentage by Weight
______________________________________
Gelose 50 64.5
Water 14.4
Glycerol 10.5
Phorate 10.6
______________________________________
Dermal toxicity tests using this formulation, a conventional synthetic
polymer formulation comprising 10% w/w phorate and pure phorate (10% w/w)
were performed on male rabbits by securing samples to the skin of the test
animals for a period of 24 hours. At the expiry of this period, rabbits
were examined for mortality and surviving rabbits observed for 14 days
before sacrifice and examination. The LD.sub.50 values are shown below in
Table 10.
TABLE 10
______________________________________
LD.sub.50 Dosage mg
Composition per kg body weight
______________________________________
Formulation of Table 2
500-1000
Synthetic polymer formulation
56-71
comprising 10% w/w phorate
Technical grade phorate (10% w/w)
5.2
______________________________________
It will be apparent to those skilled in the art from the teachings headed
that the invention may be embodied in other forms without departing from
the spirit or scope of the invention described.
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